A subcatchment is a hydrologic unit that generates runoff and produces a hydrograph that can be routed downstream. It can have two parts, pervious and impervious areas. A pervious area is a surface where water infiltrates into the upper soil zone, but in an impervious area, there is no infiltration.
Regarding your project, you can divide a study area into different subcatchments. The outlet of a subcatchment can be a node of the drainage system or another subcatchment.
|Parameter Name||Description||Default Value|
|NAME||Name of the component.||—|
|System Type||Specifies the junction’s system type, whether it belongs in the overland, storm, or sanitary system.||Blank|
|Outlet||The NHYD of the outlet node.||—|
|COMMENT 1, 2, and 3||Comment for the command.||—|
|Tag||Optional category or classification.||—|
|Area [ha]||Area of subcatchment.||5|
|*Width [m]||Width of the overland flow path (m or ft).||500|
|Slope [%]||Average surface slope (%).||0.5|
|Curb Length||Curb length (if needed for pollutant buildup functions).||0|
|Storm Index||The storm index of the storm to use with the rain gauge group.||1|
|% Imperv||Percent of impervious area (%).||25|
|N-Imper||Manning’s n for the impervious area.||0.013|
|N-Perv||Manning’s n for the pervious area.||0.1|
|Dstore-Imperv [mm]||Depth of depression storage on the impervious area (mm or in).||1.5|
|Dstore-Per [mm]||Depth of depression storage on the pervious area (mm or in).||5|
|%Zero-Imperv||Percent of the impervious area with no depression storage (%).||25|
|Subarea Routing||Choice of internal routing between pervious and impervious sub-area.||OUTLET|
|Percent Routed||Percent of runoff routed between sub-areas.||100|
|Groundwater||Groundwater flow parameters.||NO|
|Snow Pack||Name of snow pack parameter set (for snow melt analysis only).||—|
|LID Controls||LID controls||—|
|Land Uses||Assignment of land uses to subcatchment.||—|
|Initial Buildup||Initial pollutant buildup on subcatchment.||—|
*There are different methods to calculate the length and width of a basin. A simple way is the Equivalent Rectangle Method to determine the shape of the watershed.
L= (C√A+ √(C^2-1.2544A))/1.12
B= (C√A- √(C^2-1.2544A))/1.12
Which A is the area of the watershed (km^2). C is the Gravelius coefficient. L is the equivalent rectangular length (km). B is the equivalent rectangular width (km).
**There are five techniques to model the infiltration into the unsaturated soil zone in the previous area.
- Curve Number